In a network for cellular communications, the geographical area of coverage for mobile communications is subdivided into smaller areas, either logical areas or physical areas. In particular, a geographical area comprises cells and location areas.
A cell is an area in which a user can communicate with a certain base station. A location area is an area comprising a plurality of cells and it is associated with a Visitor Location Register (VLR), which stores data about all customers who are roaming within the corresponding location area.
FIG. 1 shows an example of arrangement of such areas, in which three location areas 11a, 11b and 11c are associated to respective Mobile Services Switching Centers (MSCs) 14a, 14b and 14c and in which each location area comprises a plurality of cells 12. In the figure, the areas fit complementarily with each other for the sake of simplicity, but it is clear that other arrangements known to the skilled in the art may be provided.
If an incoming transaction directed to a certain Mobile Station (MS) is received in the network (e.g. a call by another party), in order to locate the mobile station a paging request is sent to all the base stations in the location area in which the “target” mobile station is registered. When the mobile station discovers that it is being paged, a channel on the radio interface is activated, the mobile station sends a page response indicating that it has been paged and that the network can locate it.
In a location area, a great number of mobile stations is present, and the number of paging requests/responses transmitted in that location area increases with the number of mobile stations within the location area.
The increasing proliferation of mobile stations, due to the great convenience of mobile communications and the growth of additional services provided by the operators, may cause congestion in the network. In fact, the number of the available radio resources is limited and the network congestion is a drawback the operator should avoid in order not to offer services which cannot be duly handled by the network.
Moreover, requests concerning services of prime importance such as positioning request in case of emergency or law enforcement may not be served in case of congestion, this being an unacceptable drawback that greatly reduces the advantages of Location Services.
The same problem affects Location Services transactions deriving from a request for last known location of the target mobile station. Such information is usually stored at the Mobile Services Switching Center and accordingly it is straightforward for the Mobile Services Switching Center to handle such request. Again, a congestion make such a simple request unduly complicated to handle.
These drawbacks are not only unacceptable per se for a modern mobile network, but they also imply important loss of profit and disadvantages both for the operator, since the subscribers are not encouraged in taking advantage of their services, and for the subscribers, who deny themselves of useful services in which they may enroll if such services appeared to be more efficient.
At present, a mechanism for controlling the influx of calls per location area is known and it used for Call Control (CC) transactions only. In fact, for C.C. transactions, before the paging is ordered, a Roaming Number is allocated through which the call is routed from the Gateway Mobile Services Switching Center receiving the incoming call to the MSCNLR associated with the location area of the target mobile station. The known mechanism consists in defining (at the operator side) how many roaming number allocations will be permitted for a specific location area at the same time.
However no such mechanism is known for allowing the operator to control the paging flow of other transactions, such as Supplementary Services (SS), Short Message Services (SMS) and LoCation Services (LCS) transactions.
In fact, when a SS, SMS or LCS transaction is received at the MSC/VLR, a paging is ordered and the only way to control the amount of requested paging may be on network level, by controlling the file size of the software that controls the paging mechanism. This handling is however inefficient, because it does not take into account the configuration of the network, in which different location areas have different radio-resource capacities.
In addition, this mechanism cannot protect the radio network from congestion when bursts of paging requests are destined to the same location area, for example when an important athletics event or football match takes place in a stadium.